Various systems and methods for determining the range between an aircraft and an object, usually a bombing target, are well-known. These systems fall into two basic categories, active and passive. Active range-finding systems, such as radar and laser emission and detection, are considered "active systems" since they require the transmission of energy. On the contrary, "passive systems" require no such transmissions and are preferred, because it is often desired to make range measurements without the possibility of detection or interfering with other aircraft transmissions and communications.
In the past, range measurement by passive systems has been achieved using triangulation. This requires measuring the angle to the object of interest from two positions spaced a known distance. One problem with aircraft-mounted systems of this type is that the two positions must be relatively close and, hence, the accuracy of measuring long ranges is inadequate. Furthermore, this system requires added complexity since the measurements must be taken from two separate reference points, each of which must be stabilized with regard to the aircraft.
The video tracker makes use of the difference in contrast between the target and the background of a video scene to provide error signals. The error signals are sent to a servo controlled aiming platform. The aiming platform moves in the direction required to reduce the error to zero. This keeps the aiming platform pointed at the target and the target positioned at the center of the video scene. It has, therefore, been recognized that the turning rate of the stabilized aiming platform is proportional to the error signal from the video tracker and the turning rate with regard to the target object can easily be determined.
There have been prior uses of automatic video trackers for supplying turning rate information to determine proper ordnance release; however, these have included extremely complicated systems in which range measurement was not required or desired. Such a prior use is described in U.S. Pat. No. 3,699,310 issued to Roy D. Cole, entitled "Angular Rate Bombing System".
The most pertinent other patent prior art of which the applicant is aware includes U.S. Pat. No. 3,162,103 issued to James M. Perkins, entitled "Photographic Method for Locating Objects that Drift at Sea"; U.S. Pat. No. 4,983,033 issued to Koji Suzuki, entitled "Automatic Range Finder for Camera"; U.S. Pat. No. 5,001,508 issued to Kimiski Ogawa, entitled "Range Finder"; and U.S. Pat. No. 5,060,004 issued to Kiyoshi Ikuta, entitled "Distance Measuring Device". These additional prior art references are pertinent to the present invention in that they show various range-finding systems. However, none shows the use of an automatic video tracker or use on an air vehicle for determining a range to ground objects or other slower moving vehicles.